Stereo Preamplifier Guide
A Look At Tube, Digital, and Solid State Preamps
In a home audio system, a stereo preamplifier is the box which takes the outputs from various sources (Compact disc player, record deck, tape deck, radio) and provides a volume control. As the name "preamplifier" suggests, it is something that comes before the proper amplifier (the Power amplifier).
The preamplifier provides some voltage boost (e.g. from 10 millivolts to 1 volt) but no significant current gain. The power amplifier provides the higher current necessary to drive loudspeakers.
Types of Stereo Preamplifiers
- Solid State Preamps: The solid state stereo preamp is the most common. It uses transistors to boost the signal from low level to a voltage that a power amplifier can deal with.
- Tube Preamps / Valve preamps (British English): The tube preamp uses vacuum tubes (or "valves") to boost the signal in an audio system. A tube preamp needs to have the vacuum tubes replaced periodically.
- Digital Preamps (with DACs): A new category of preamp is the digital preamp. Unlike tube preamps and solid state preamps they can accept a digital audio signal from products like an iPod, a PC or a CD transport. The internal Digital to Analog Converter (DAC) converts the digital signal to analog, and then boosts it for the power amp.
Learn more about Digital to Analog converters
When do you need a stereo preamplifier?
You need a stereo preamp when you want to step up the home audio quality ladder, from a normal "integrated" amplifier (ie. a one-box amplifier).
If all your music is stored on your PC / iPod, or your CD transport has a "digital output socket", then a digital stereo preamplifier is the way to go. You get a high quality DAC as well as preamplifier all in one box.
On the other hand, if you still have cherished vinyl records and a record deck, you should look at a solid state or tube preamp.
What's the difference? Many music lovers claim that tube amplifiers sound "warmer" and more musical. This sounds a bit like black magic!
But there is a grain of truth in there. When you have the volume turned up for your favorite piece of music, and suddenly there's a really loud bit, a solid-state amplifier cannot cope. The extreme volume is "clipped" and the circuits put out what is called a "square wave", which sounds harsh to our ears.
With a tube amplifier, the vacuum tubes also do not cope with the extremes of volume. But they "fail" in a different way. They start to produce harmonics, which is much more musical to human ears.
So, you really only hear the difference clearly at extreme volumes, although there are elements of the "tube effect" at all volume levels.
Which stereo preamplifiers offer best value for money?
At entry-level it's worth checking out products from NAD (the C-165), and Emotiva (the USP-1).
In the mid-range, from $1000 to $2000, look at the Quad QC-24 and the Cambridge Audio 840 E. The Naim NAC 152 also sneaks into this price territory!
Above this level, there are the usual suspects from Krell, Mark Levinson, McIntosh, Meridian, and others.
As always, you should audition the preamp you are interested in against models that are significantly LESS expensive as well as MORE expensive.
Tell the dealer to hide which preamp you are listening to. Can you hear a difference?
The most accurate way to do this is with high quality headphones plugged straight into the stereo preamplifrer. There will be no "side effects" from power amplifiers, loudspeakers or room acoustics to muddy the picture. Happy listening!
Related article: home audio amplifiers primer.
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